The present invention relates to systems for monitoring the configuration of surfaces. In particular it is an interferometric system for sensing the figure, ie. the surface configuration, of optical systems such as the optics of a telescope, for monitoring the surface so as to detect any deviation from the desired configuration caused for example, by warping.
In accordance with known techniques for optical figure sensing collimated light from a laser source is directed to the optical surface from which it is reflected to an interferometer. In the interferometer light reflected from the optical surface is combined with a reference beam of light and the interference pattern thus produced is compared with a reference interference pattern which was generated when the subject optical element had the desired configuration; mismatch of the interference patterns thus indicates distortion of the surface.
Previously known systems for figure sensing optical elements having curved surface areas customarily collect reflected light at a conjugate, e.g., center of curvature, of the optical element, and thus, such systems usually require partial dismantling of the optical system being tested in order to mount the figure sensing apparatus in operative position relative to the optical element being tested.
Principal objects and advantages achieved by the system of the present invention are the provision of an optical figure sensing system that is adapted for sensing the surface configuration at a number of different points thereon so as to reveal the specific area at which distortion occurs as well as the amount of such distortion. Moreover, this system is so constituted that the position at which light is collected for the interferometer portion of the system is not critical; it does not have to be collected at the center of curvature of a curved optical element being tested. Consequently, this system is adapted to be primarily mounted in operative position within an optical system so as to be instantly operable for testing the optics without having to disassemble the optical system. Thus an optical figure sensing system in accordance with this invention has the particular advantage that it may be mounted in an optical system, as an optical system carried in a space vehicle, for monitoring the critical surfaces of the optical system at desired intervals for checking the accuracy of the system; if distortion is detected, information provided by the figure sensing system as to the location and amount of distortion may be applied for correcting the distortion of optical elements which are flexible or semi-flexible by actuating and controlling the operation of rams or other suitable mechanism for moving selected areas of the optical elements as required to restore or achieve the desired configuration.